Solid state d.c. circuit breaker



April 11, 1967 R L. WHITE 3,313,985

SOLID STATE D.C. CIRCUIT BREAKER Filed April 5, 1964 INVENTOR. RICHARD L. WHITE ATTORNEY United States Patent 3,313,985 SOLID STATE D.C. CIRCUIT BREAKER Richard L. White, Glendora, Califi, assignor to Dickson Electronics Corporation Filed Apr. 3, 1964, Ser. No. 357,253 6 Claims. (Cl. 317-33) The present invention pertains to circuit breakers, and more specifically, to circuit breakers of the type for interrupting a direct current when a predetermined circuit condition exists.

The complexities of modern electronic systems have placed a burden upon circuit breakers for effectively interrupting current flowing to the delicate components of the electronic system. Fast acting, direct current circuit breakers are required that present a low voltage drop when inserted in series with a load and which are compatibly sized in relation to the rest of the electronic com ponents. The small physical size of present systems therefore dictates that a circuit breaker shall be compact; further, the interrelationship and the small spacing involved in modern systems requires that the circuit breaker present no radio frequency interference during circuit breaker operation. Reliability and long life are also requirements, particularly in those applications where the circuit breaker is to be located at an inaccessible location.

Accordingly, it is an object of the present invention to provide a direct current circuit breaker that is physically small while nevertheless being reliable and having a long life.

It is another object of the present invention to provide a direct current circuit breaker utilizing the advantages to be gained through the use of solid state devices and inexpensively providing trip speeds faster than those available in circuit breakers of the prior art.

It is a further object of the present invention to provide a direct current circuit breaker that is not inductive and will not produce any radio frequency interference when interrupting the circuit in which it is connected.

It is still another object of the present invention to provide a direct current circuit breaker that is electronically resettable and that has a low voltage drop and power dissipation in operation.

Further objects and advantages of the present invention may become apparent to those skilled in the art as the description thereof proceeds. The invention, and the operation thereof, may more readily be described by reference to the accompanying drawings in which:

FIGURE 1 is a block diagram of a direct current circuit using the circuit breaker of the present invention.

FIGURE 2 is a schematic circuit diagram of a circuit breaker constructed in accordance with the teachings of the present invention.

FIGURE 3 is a volt-ampere curve of a typical tunnel diode useful for describing the operation of the circuit of FIGURE 2. I

FIGURE 4 is a schematic circuit diagram of another circuit breaker constructed in accordance with the teachings of the present invention.

FIGURE 5 is a volt-ampere characteristic curve of a typical zener'diode useful for describing the operation of the circuit of FIGURE 4.

Referring to FIGURE 1, a source of DC. potential (not shown) is connected to terminals and 11. Terminal 10 is indicated in FIGURE 1 as being the positive terminal and is connected to a circuit breaker by connecting the terminal 10 to the circuit breaker terminal 16. The opposite side of the circuit breaker 15 is connected by terminal 17 to a load indicated generally in FIGURE 1 at 19. The opposite side of the load 19 is connected to the terminal 11 thereby completing the circuit. The circuit breaker 15 may provide overload protection for the load 19 by detecting an excessive current (and opening the circuit) or by detecting an over-voltage (and opening the circuit). To facilitate the detection of an over-voltage, the circuit breaker 15 may be connected as indicated by the dotted line 20 to the node 21.

Referring to FIGURE 2, the circuit breaker 15 of FIGURE 1 is shown in greater detail. The circuit breaker 15 includes terminals 16 and 17 for connection to the positive line terminal and to the positive side of, Y

the load. The anode of a diode 25 is connected to the terminal 16 and has the cathode electrode thereof connected to the collector electrode 26 of a transistor 27. The emitter electrode 28 of the transistor is connected via line 29 to the terminal 17. The base electrode of the transistor 27 is connected by conductor 36 to the collector electrode 36 of a second transistor 37. The emitter electrode 38 of the second transistor is connected through a tunnel diode 40 and a conductor 41 to the terminal 16. The base electrode of the transistor 37 is connected through conductor 43 to the collector electrode 26 of the transistor 27. A capacitor 45 is connected by conductor 46 to the emitter electrode 38 of transistor 37 and is connected by conductor 47 to the terminal 17.

The operation of the circuit of FIGURE 2 may best be described by first referring to the curve shown in FIGURE 3. The tunnel diode 40 is a non-linear device that exhibits a negative resistance along a portion of its volt-ampere characteristic. The characteristic of FIG- URE 3 is intended to be illustrative of a typical tunnel diode. The portion 50 of the curve of FIGURE 3 represents the positive resistance of the tunnel diode for currents initially passing through the diode having a magnitude somewhere between I and I If the current exceeds the peak current I the tunnel diode exhibits a negative resistance as indicated by the portion 51 of the curve of FIGURE 3. Thus, if current passes through the tunnel diode and exceeds I the voltage drop across the tunnel diode will jump from the positive resistance portion 50, to the second positive resistance portion 52, or in other words will switch from a low to a high voltage state. Referring now to FIGURE 2, it will be assumed that current is flowing from the terminal 16 to the terminal 17 and that the load connected to the terminal 17 is behaving properly. Current will thus flow from the terminal 16 through the tunnel diode 40 to the complementary transistors 27 and 37. Current will also flow from the terminal 16 through the diode 25 to the two transistors. The current carried by the circuit breaker from terminal 16 to terminal 17 thus passes through the two transistors and is carried from the base of transistor 37 to the collector of transistor 27 and from the collector of transistor 37 to the base of transistor 27. The circuit will continue to operate in this manner and the bias provided to the transistor 37 by the diode 25 and tunnel diode 40 Will assure the closed condition of the circuit breaker. The voltage drop exhibited by the circuit breaker is only the forward voltage drop of the diodes and the saturation voltage of the transistors; further, the components described will provide very low power dissipation. If the load circuit connected to the terminal 17 should fail and become shortcircuited, the current surge caused by the load failure will be transmitted from the terminal 17 through the capacitor 45 to the cathode of the tunnel diode 40. The sudden current increase will cause the tunnel diode to switch from the low voltage to the high voltage state thereby removing the forward bias on the transistor 37. Transistor 37 begins to shut off thereby decreasing the biasing provided to the base electrode of transistor 27. The feed-back provided by transistor 27 to the base electrode of the transistor 37 through the collector electrode 26 further tends to shut transistor 37 off. The

total effects of the current surge are cumulative until both transistors 27 and 37 are rapidly cut off. The circuit breaker has thus opened and the circuit between terminals 16 and 17 has been interrupted. The circuit breaker of FIGURE 2 may be reset in several ways, and the circuit of FIGURE 4 is intended to illustrate two such methods.

Referring to FIGURE 4, the circuit of FIGURE 2 has been incorporated therein and like elements are referenced by like numerals. When the circuit breaker is in its open condition, the transistors 27 and 37 may appropriately be gated to their conducting state (that is, reset) by applying an appropriately poled electronic pulse to the terminal 55 which is transmitted to the base of transistor 27 and the collector of transistor 37. To mechanically reset the circuit breaker of FIGURE 4, a pushbutton switch 70 is connected to the base electrode of the transistor 37 and to the terminal 16 through a capacitor 71. A resistor 72 connects the switch 7 to the terminal 17. The operation of the manual reset of FIGURE 4 may be described as follows. When the circuit breaker is open, thecapacitor 71 charges to approximately line voltage. When the switch 70 is closed, the capacitor charge provides an appropriate bias to gate the transistor 37 on. As transistor 37 begins to conduct, the cumulative action of the complementary pair (transistors 27 and 37) quickly gate both transistors to their full on condition thereby closing the circuit breaker and establishing a low resistance direct current circuit between terminals 16 and 17.

A resistor 61 connects the base electrode of the transistor 27 and the collector electrode of the transistor 37 to the terminal 17; a resistor 60 connects the same node to the cathode of a zener diode 62. The anode of the .zener diode 62 is connected by the conductor 20 to node predetermined zener voltage is obtained. At that instant,

the diode no longer presents a current block and incremental'resistance drops to a very low value. Referring once again to FIGURE 4, the node 21 will be recognized as the node 21 of FIGURE 1. It may therefore be recognized that the voltage existing between terminals 17 and node 21 is, in fact, the load voltage. If the supply voltage should increase, or a transient voltage superimposed on the supply voltage should occur, the voltage increase resulting therefrom will impress a rapid voltage increase between points 17 and 21. This voltage surge is a negative voltage impressed on the zener diode 62 that exceeds the zener voltage thus permitting current to flow through the diode from terminal 17. This instantaneous current fiow results in a triggering of the circuit breaker through the capacitor 45 in a manner similar to the triggering that occurred from a sudden current increase. The sudden current transient triggers tunnel diode 40 to its high voltage state and initiates the cumulative cut-off procedure for the circuit breaker. Thus, the circuit breaker of FIGURE 4 will rapidly open in the event of a current overload (such as that occurring in the case of a shortcircuit) or in the event of an overvoltage. The tunnel diode 40 of FIGURES 2 and 4 may be replaced by any voltage dropping device such as a resistor; however, the tunnel diode presents unique advantages in that the trip point of the circuit breaker may more readily be predicted and reproduced without the otherwise necessity of careful calibration of transistors 27 and 37. The zener diode 62 may also be replaced by other voltage sensitive devices; however, as in the case with the tunne o e,

the zener diode is particularly advantageous and dependable for the present application. The transistors 27 and 37 are shown in FIGURES 2 and 4 as NPN and PNP transistors respectively, it being understood that the transistors may be reversed as long as they remain complementary. It may thus be seen that the DC. solid state circuit breaker of the present invention provides a circuit breaker having no inductive component, that is physically small, reliable, does not present any radio frequency interference problems, has a trip speed limited only by the ability of the transistors 27 and 37 to be cut 01f, is electronically or manually resettable, and exhibits a low voltage drop and power dissipation when in the closed position. It will be apparent to those skilled in the art that many modifications may be made of the present invention without departing from the spirit and scope thereof.

I claim:

1. In a solid state D.C. circuit breaker the combination comprising:

(a) a first and a second transistor each having a collector electrode, an emitter electrode, and a base electrode, said transistors being of complementary yp (b) means connecting the collector electrode of each transistor to the base electrode of the other transistor;

(c) a capacitor connected between the emitter electrodes of said transistors;

(d) a first and a second terminal;

(e) a device exhibiting a negative resistance along only a portion of its volt-ampere characteristic connected in series between said first terminal and the emitter electrode of said first transistor;

(f) a voltage dropping device connected in series between said first terminal and the base electrode of said first transistor, and

(g) means connecting the emitter electrode of said second transistor to said second terminal.

2. In a solid state D.C. circuit breaker the combination comprising:

(a) a first and a second transistor each having a col"- lector electrode, an emitter electrode, and a base electrode, said transistors being of complementary yp (b) means connecting the collect-or electrode of each transistor to the base electrode of the other transistor;

(c) a capacitor connected between the emitter electrodes of said transistors;

(-d) a first and a second terminal;

(e) a tunnel diode connected in series between said first terminal and the emitter electrode of said first transistor;

(f) a voltage dropping device connected in series between said first terminal and the base electrode of said first transistor, and

(g) means connecting the emitter electrode of said second transistor to said second terminal.

3. In a solid state D.C. circuit breaker the combination comprising:

(a) a first and a second transistor each having a collector electrode, an emitter electrode, and a base electrode, said transistors being of complementary yp (b) means connecting the collector electrode of each transistor to the base electrode of the other transistor;

(c) a first and a second terminal;

(d) a device exhibiting a negative resistance along only a portion of its volt-ampere characteristic connected in series between said first terminal and the emitter electrode of said first transistor;

(e) a diode connected in series between said first terminal and the base electrode of said first transistor, and

(f) means connecting the emitter electrode of said second transistor to said second terminal.

4. In a solid state D.C. circuit breaker the combination comprising:

(a) a first and a second transistor each having a collect-or electrode, an emitter electrode, and a base electrode, said transistors being of complementary yp (b) means connecting the collector electrode of each transistor to the base electrode of the other transistor;

(c) a capacitor connected between the emitter electrodes of said transistors;

(d) a first and a second terminal;

(e) a tunnel diode connected in series between said first terminal and the emitter electrode of said first transistor;

(f) a diode connected in series between said first terminal and the base electrode of said first transistor, and

(g) means connecting the emitter electrode of said second transistor to said second terminal.

5. In a solid state D.C. circuit breaker the combination comprising:

(a) a first and a second transistor each having a collector electrode, an emitter electrode, and a base electrode, said transistors being of complementary types;

(b) means connecting the collector electrode of each transistor to the base electrode of the other transistor;

(c) a capacitor connected between the emitter electrodes of said transistors;

(d) a first and a second terminal;

(e) a tunnel diode connected in series between said first terminal and the emitter electrode of said first transistor;

(f) a diode connected in series between said first terminal and the base electrode of said first transistor;

(g) means connecting the emitter electrode of said second transistor to said second terminal, and

(h) resetting means connected to said transistors to gate them to conduction when they are in a non-conducting state.

6. In a solid state D.C. circuit breaker the combination comprising:

(a) a first and a second transistor each having a collector elect-rode, an emitter electrode, and a base electrode, said transistors being of complementary types;

(b) means connecting the collector electrode of each transistor to the base electrode of the other transistor;

(c) a capacitor connected between the emitter electrodes of said transistors;

(d) a first and a second terminal;

(e) a tunnel diode connected in series between said first terminal and the emitter electrode of said first transistor;

(f) a diode connected in series between said first terminal and the base electrode of said first transistor;

(g) means connecting the emitter electrode of said second transistor to said second terminal;

(11) a load having an input terminal and an output terminal;

(i) means connecting the input terminal of said load to said second terminal, and

(j) a zener diode connected between the emitter electrode of said first transistor and the output terminal of said load.

References Cited by the Examiner UNITED STATES PATENTS 2,864,904 -12/ 1958 Jensen.

2,962,603 1 H1960 Bright 317-33 X 3,176,163 3/1965 Tiemann.

3,181,032 4/1965 Myers 3 17 -33 3,204,175 8/ 1965 Ku-riger 317-22 X MILTON O. HIRSHFIELD, Primary Examiner. R. V. LUPO, Assistant Examiner. 

1. IN A SOLID STATE D.C. CIRCUIT BREAKER THE COMBINATION COMPRISING: (A) A FIRST AND A SECOND TRANSISTOR EACH HAVING A COLLECTOR ELECTRODE, AN EMITTER ELECTRODE, AND A BASE ELECTRODE, SAID TRANSISTORS BEING OF COMPLEMENTARY TYPES; (B) MEANS CONNECTING THE COLLECTOR ELECTRODE OF EACH TRANSISTOR TO THE BASE ELECTRODE OF THE OTHER TRANSISTOR; (C) A CAPACITOR CONNECTED BETWEEN THE EMITTER ELECTRODES OF SAID TRANSISTORS; (D) A FIRST AND A SECOND TERMINAL; (E) A DEVICE EXHIBITING A NEGATIVE RESISTANCE ALONG ONLY A PORTION OF ITS VOLT-AMPERE CHARACTERISTIC CONNECTED IN SERIES BETWEEN SAID FIRST TERMINAL AND THE EMITTER ELECTRODE OF SAID FIRST TRANSISTOR; (F) A VOLTAGE DROPPING DEVICE CONNECTED IN SERIES BETWEEN SAID FIRST TERMINAL AND THE BASE ELECTRODE OF SAID FIRST TRANSISTOR, AND (G) MEANS CONNECTING THE EMITTER ELECTRODE OF SAID SECOND TRANSISTOR TO SAID SECOND TERMINAL. 